In optical fiber technology light signals are used in place of electrical signals to transmit information from one place to another. In the place of metal wires, transparent optical fibers carry light signals bearing the transmitted information.
One of the desired components in fiber optic technology is a low cost, high-performance coupler by which light signals sent on one optical fiber may be divided or split into light signals on several optical fibers. Conversely in some splitter/couplers light signals on more than one optical fiber may be combined into one fiber by such a coupler. This is a straightforward matter in the more common electrical technology. Wires may be spliced together to form multiple branches. Electrical signals sent along one wire will naturally propagate along all branches connected to the wire; and the converse situation is also true.
In fiber optic technology the dividing and combining of the light signals is a more complex. Connections must be made very carefully to ensure that the light signals are distributed to the fiber branches with minimum loss in intensity. Hence various schemes for optical couplers have been devised.
Heretofore, integrated optical waveguides, fused fiber optic star couplers, slab wave guides, active couplers (either acting as combiners or splitters), optical hologram or Fourier transform fiber optic splitters, and GRIN lens fiber optic splitters have been investigated. However, many of these approaches have had deficiencies of performance, such as in excess loss, loss deviation, frequency response, phase preservation and expandability of the splitting ratio, and costs, such as in fabrication of the splitter or interconnection with the rest of a fiber optic network.
Couplers are some of the most ubiquitous of all passive discrete optical components found in most optical communication systems. However until now, individual discrete couplers have been used. Thus, there is a need for a single device that will provide the function of multiple coupling devices in a single coupling element.
U.S. Pat. No. 5,371,816 in the name of Jing-Jong Pan, assigned to E-Tek Dynamics, Inc. proposes a 1:N optical coupler where N can be an arbitrary number such as 16 or greater. Although this invention appears to perform its intended function, it is rudimentary and limited in its functionality, simply allowing a signal propagating on an input fiber to be split into multiple output fibers or conversely allowing signals carried on a plurality of ports, to be combined on a single optical fiber.
In some instances splitters, couplers and mulitiplexors or demultiplexors are combined to form optical devices with desired functionality. However, as the number of input an output ports increase, the complexity, size and cost of these combined devices increases proportionally. And yet still further, such optical circuit may become unwieldy with regards to maintenance or repair as the number of ports increases.
For example, a splitter combiner/multiplexor that is to perform the function of splitting an optical signal of a first wavelength .lambda.1 into 16 sub-signals of wavelength .lambda.1, and combining each of these sub-signals with waveguides carrying a second wavelength .lambda.2, can be configured using a plurality of 1.times.2 splitters and 16 wavelength multiplexing filters for combining each of the 16 sub-signals of wavelength .lambda.1 with the 16 signals having the second wavelength .lambda.2. Of course, in such a device, now commercially available, the losses resulting from each coupling, for example each splitter and filter node, are considerable, and cumulative. Furthermore, the cost of providing a device that has plurality of 1.times.2 splitters and 16 WDM couplers is quite substantial. The size of such a device is also considerable and prognosis for easy maintenance and repair is not good.
Thus, it would be advantageous to have a low loss efficient, compact device that provided such functions as wavelength dependent or independent splitting, and/or coupling, or, splitting, and/or coupling in a wavelength dependent manner; Furthermore, it would be advantageous to have a device that could utilize a substantial region of the useful end surface area of a collimating lens, such as a GRIN lens to provide the splitting of optical signals. The embodiments of the instant invention endeavor to provide such functionality.
It is therefore an object of this invention to overcome the limitations of many of the prior art devices and to attempt to provide the desired functionality described heretofore.
It is a further object of the invention to provide an arrangement of linear arrays of optical fibres that are easily coupled with a lens and that can be easily tuned to perform optical alignment of pairs of waveguides by moving a single block housing linear arrays comprising pairs of waveguides.